What is the difference between the | and || operators?

| is a bitwise or, || is a boolean or.

Meaning

| is binary operator, it will binary OR the bits of both the lefthand and righthand values.

|| is a boolean operator, it will short circuit when it encounters 'true' (any non-zero value, this includes non-empty arrays).

Examples

print_r(1 | 2)  // 3
print_r(1 || 2) // 1

When used with functions:

function numberOf($val) {
    echo "$val, ";
    return $val;
}

echo numberOf(1) | numberOf(2);  // Will print 1, 2, 3
echo numberOf(1) || numberOf(2); // Will print 1, 1

Just like the & and && operator, the double Operator is a "short-circuit" operator.

For example:

if(condition1 || condition2 || condition3) If condition1 is true, condition 2 and 3 will NOT be checked.

if(condition1 | condition2 | condition3) This will check conditions 2 and 3, even if 1 is already true. As your conditions can be quite expensive functions, you can get a good

performance boost by using them.

There is one big caveat, NullReferences or similar problems. For example:

if(class != null && class.someVar < 20) If class is null, the if-statement will stop after "class != null" is false. If you only use &, it will try to check class.someVar and you get a

nice NullReferenceException. With the Or-Operator that may not be that much of a trap as it's unlikely that you trigger something bad,

but it's something to keep in mind.

No one ever uses the single & or | operators though, unless you have a design where each condition is a function that HAS the be

executed. Sounds like a design smell, but sometimes (rarely) it's a clean way to do stuff. The & operator does "run these 3 functions,

and if one of them returns false, execute the else block", while the | does "only run the else block if none return false" - can be useful,

but as said, often it's a design smell.